Lamp and method of manufacturing a lamp

ABSTRACT

A lamp comprising an elongate light source and a coaxially transparent sleeve surrounding the light source, wherein the light source is fixed at one end in the sleeve by means of a cured cement, wherein a cement barrier is present between the light source and the sleeve for preventing the cement in its uncured state from entering the middle portion of the lamp, and wherein said cemenit barrier is made of a somewhat flexible material.

The invention relates to a lamp comprising an elongate light source anda coaxially transparent sleeve surrounding the light source.

Such a lamp is described in EP-A-0 336 478. In the known lamp, the lightsource and the sleeve are both mounted in a base. Such transparentsleeves have to be able to withstand the high temperatures occurring inlamps and thus are in general made of glass, quartz glass or quartz.Although it is not described how the light source and the sleeve aremounted in said base, it can be seen that the base, which comprises thecurrent supply conductors, is relatively large, which is disadvantageousfor its reliability. The invention aims at a more compact and reliablemounting solution.

To that end, the light source is fixed at one end in the sleeve by meansof a cured cement, wherein a cement barrier is present between the lightsource and the sleeve for preventing the cement in its uncured statefrom entering the central portion of the sleeve, and said cement barrieris made of a non-metallic somewhat flexible material. Preferably, saidlight source and said sleeve are mounted on a ceramic base by means ofthe preferably ceramic cement, and preferably also a reflector ismounted on said base by means of the cement. In this manner a verycompact lamp base can be obtained, in which the position of the lightsource can be maintained in a very reliable and precise manner. Also thecurrent supply conductors are safely enclosed in said cement.

The cement barrier should have some flexibility, because it was foundthat the sleeves or the burners tended to crack very often when a metalcement barrier was used. The cracking was mainly caused by the largedifference in thermal expansion between the metal cement barrier and thequartz or quartz glass sleeve, and the forces that are applied to thequartz or quartz glass sleeve thereby. Therefore, the term flexibilityshould be interpreted as being more flexible and/or softer than glass,quartz glass and quartz. If a material having flexibility (calledflexible material) is used, these forces will be easily absorbed.

Preferably, the non-metallic flexible material retains its shape attemperatures above 150° C., preferably above 200° C., more preferablyabove 250° C. In a preferred embodiment said non-metallic material has asmooth surface towards the cement, which counteracts adherence of thecement on to the cement barrier material. Suitable materials are micaand various synthetic materials or plastics. In particular mica has beenfound very useful, because it can easily withstand lamp temperatures upto 400° C. Also the cement will not adhere to the mica plate, which is afurther advantage in avoiding high stresses.

In a further preferred embodiment the flexible material of the cementbarrier has a fibrous surface towards the cement. Because of the fibrousstructure of the said materials the surface facing the cement will forma barrier to which the cement may adhere and at the same time thesurface will easily absorb differences in thermal expansion and thusavoid the built up of thermal stresses between the different parts. Inparticular glass wool or ceramic wool have turned out to be suitablefibrous materials from which the non-metallic cement barrier can beformed.

In yet a further preferred embodiment the flexible material is formed bya synthetic material. An advantage of synthetic material is the veryvast amount of available materials from which a selection can be made.Important in the selection is that the selected material has thesuitable thermal properties to persistently withstand temperatures of150° C. and more. Very suitable in this respect ispolytetrafluoroethylene (PTFE).

In a preferred embodiment, said light source comprises a ceramic burner,and said sleeve is made of quartz glass or quartz.

The invention furthermore relates to a method of manufacturing a lampwherein an elongate light source is coaxially inserted in a transparentsleeve, wherein a cement barrier made of a somewhat flexible material isplaced between the light source and the sleeve, and wherein a liquidcement is poured onto said barrier for fixing said light source in saidsleeve.

The above and further aspects of the invention will be illustrated withreference to the drawings, wherein

FIG. 1 is a cross-section of a lamp unit according to the invention,

FIG. 2 shows another embodiment of the lamp unit according to theinvention, and

FIG. 3 is a plan view of a cement barrier used in the lamp unitaccording to the invention.

In FIG. 1, a lighting unit 1 is provided with a concave reflector 2having an axis of symmetry 3 and a light emission window 21 bounded by acircumferential edge 20 of the reflector transverse to said axis, withan elongate light source 30 axially arranged substantially symmetricallyon the axis of symmetry and accommodated in a holder 4 opposite thelight emission window, and with an axially positioned cap 5 serving asan optical screening means that partly surrounds the light source forintercepting unreflected light rays. The light source is surrounded by asleeve 60 having an end 61 that faces the light emission window. The cap5 is positioned over the sleeve adjacent an end thereof by means of alocking element 70 provided at the sleeve. In the embodiment shown, thelight source is formed by a ceramic discharge vessel 31 which isprovided with external closing plugs 320, 330 at respective axial endfaces 32, 33 for positioning lead-through elements to electrodesarranged in the discharge vessel, between which electrodes a dischargeextends in the operational condition. This is a metal halide dischargein the example described. The discharge vessel is accommodated in anouter bulb 34. The outer bulb 34, sleeve 60, and reflector 2 areindetachably connected to one another at the area of the holder 4 in thecase described. The reflector and the light source have thus beenintegrated into a metal halide lamp.

The sleeve 60 is a tubular body of hard glass over which the cap 5 hasbeen passed at the area of the end 61. The cap is provided with ascreening ring 51 at the side facing away from the light emissionwindow, which ring extends radially away from the light source over adistance d. The positioning of the screening ring effectively preventsan unreflected emission of light originating from that portion of thelight source that is situated between the cap and the holder. Thescreening ring is provided with a ring edge 52, and the locking element70 is provided with a tag-shaped element 71 that grips into the ringedge under spring force in a direction radially away from the lightsource. At least one recess 62 is provided in an outer surface 6 of thesleeve 60, into which a portion of the locking element 70 grips underspring force.

FIG. 2 shows a further advantageous embodiment in which the holder 4 isprovided with a base 8 with electrical connection contacts forconnecting an electrical supply source.

The reflector and the light source are preferably indetachably connectedto one another so as to form a lamp, preferably at the area of theholder 4.

In FIG. 2, the holder 4 is provided with a locking mechanism 41 adjacenta connection to the light source 34 and the sleeve 60 in the form of anindentation close to an end of the holder 4. This indentation is shapedsuch that the coupling between the reflector on the one hand and thelight source and sleeve on the other hand remains intact in spite ofdifferences in expansion during operation of the light source. Veryfavorable is a situation in which three indentations 41 are provided atequal mutual distances on the circumference of the relevant end of theholder.

The base 8, holder 4 and sleeve 60 are joined to a seal 341, for examplein the form of a pinch, of the light source by means of a cured cement80. The base 8 is provided with a filling hole 81 and a rise hole 811for providing the cement in its uncured form, that is the still liquidcement mass. In a manner known per se, the cement mass is cured byheating into cured cement 80, whereby the joint mentioned above iscreated. The choice of a filling circumference 82 for the filling hole81 greater than an exit circumference 821 advantageously achieves thatthe cement 80 in the cured state forms an interlocking fixture. This isrealized in the embodiment shown in that the filling hole 81 has atapering gradient in cross-section. The interlocking effect is furtherenhanced in that the rise hole 811 also has a tapering gradient with agreatest diameter at the side remote from the holder 4.

A plate 83 extending circumferentially at least substantially up to thewall of the sleeve 60 is arranged around the seal 341 of the lightsource. FIG. 3 is a plan view of the plate 83. This plate serves to stopthe uncured cement, that is the still liquid cement mass 80 duringfilling. Thus the plate 83 forms the cement barrier. The plate 83 shouldbe heat resistant, preferably up to 150°, more preferably up to at least200°, even more preferably up to at least 250°. In one aspect of theinvention, the cement 80 should preferably not adhere to the plate 83,otherwise cracks could arise owing to a difference in coefficient ofexpansion. Consequently the material of the plate 83 has preferably asmooth surface towards the cement. In another aspect of the inventionthe material of the plate 83 has a fibrous surface towards the cement80, which it is true will promote adherence of the cement. However,differences in coefficient of expansion will then easily by absorbed bythe fibrous structure of the material. Furthermore, the material shouldpreferably not be too rigid, because otherwise the plate 83 coulddestroy the glass of the seal 341 or the sleeve 60 by pressure. Anotherproperty the material should preferably have is that it is not toobrittle.

Metals were accordingly found to be not particularly suitable materialsfor the plate 83. Consequently the material of plate 83 should besomewhat flexible, at least more flexible than metal and than glass,quartz glass and quartz. A very suitable non-metallic material was foundto be mica. Glass wool as a fibrous non-metallic material also turns outto be a suitable material as well as ceramic wool. Other examples ofnon-metallic materials from which the plate may preferably bemanufactured are various synthetic materials such like phenolic andunsaturated polyester resins, polyamide, flexible PVC, polyesterthermoplastic elastomer (TPE), olefinic TPE, polyester alloy,thermoplastic polyimide, acrylic and epoxy resins, fluoropolymers, forinstance polytetrafluoroethylene (PTFE), styrenic resins, and polyestercarbonate.

1. A lamp comprising an elongate light source and a coaxiallytransparent sleeve surrounding the light source, wherein the lightsource is fixed at one end in the sleeve by means of a cured cement,wherein a cement barrier is present between the light source and thesleeve for preventing the cement in its uncured state from entering thecentral portion of the sleeve, and wherein said cement barrier is madeof a non-metallic flexible material.
 2. A lamp according to claim 1,wherein said material retains its shape at temperatures above 150° C. 3.A lamp according to claim 1, wherein said non-metallic material has asmooth surface towards the cement, which counteracts adherence of thecement on to the cement barrier material.
 4. A lamp according to claim1, wherein said non-metallic material is mica.
 5. A lamp according toclaim 1, wherein said non-metallic material is a synthetic material. 6.A lamp according to claim 1, wherein said non-metallic material of thecement barrier has a fibrous surface towards the cement.
 7. A lampaccording to claim 1, wherein said non-metallic material is glass woolor ceramic wool.
 8. A lamp according to claim 1, wherein said lightsource and said sleeve are mounted on a ceramic base by means of thecement.
 9. A lamp according to claim 1, wherein a reflector is mountedon said base by means of the cement.
 10. A lamp according to claim 1,wherein said light source comprises a ceramic burner.
 11. A lampaccording to claim 1, wherein said sleeve is a made of quartz glass orquartz.
 12. A method of manufacturing a lamp, wherein an elongate lightsource is coaxially inserted into, a transparent sleeve, wherein acement barrier made of a flexible material is placed between the lightsource and the sleeve, and wherein a liquid cement is poured onto saidbarrier for fixing said light source in said sleeve.
 13. The lamp ofclaim 2, wherein said material retains its shape at temperatures above200° C.
 14. The lamp of claim 2, wherein said material retains its shapeat temperatures above 250° C.